A conventional intake control device for an internal combustion engine controls opening degree of a throttle valve at a predetermined opening degree by operating a motor in accordance with an accelerator position operated by a driver.
The clearance between the surface of a throttle bore of a throttle body and the outer periphery of the throttle valve, when the throttle valve is in a full-closing position, exerts a large influence to a performance in air tightness of the intake control device. Therefore, the clearance between the surface of the throttle bore of the throttle body and the outer periphery of the throttle valve needs to be accurate in dimension. The intake control device may be used in a cold climate such as winter. Moisture may be contained in intake air drawn into respective cylinders of the engine through an intake pipe accommodating the throttle body. Moisture contained in intake air may adhere to the surface of the throttle valve, and the moisture may be cooled. When the moisture is frozen throughout the surface of the throttle bore and the outer periphery of the throttle valve, the throttle valve may stick to the surface of the throttle bore of the throttle body. Accordingly, the throttle valve needs to be restricted from being frozen.
As shown in FIG. 5, a throttle body 101 has an internal double-pipe structure, which is constructed of a bore inner pipe 102 and a bore outer pipe 103, according to U.S. Pat. No. 5,704,335 (JP-A-09-032590), for example.
Intake air flows into the respective cylinders of the engine through the bore inner pipe 102. The bore outer pipe 103 is arranged on the radially outer side of the bore inner pipe 102 to form an annular space therebetween. The bore inner pipe 102 is floated from the bore outer pipe 103, which constructs the outer shell of the throttle body 101, so that moisture, which flows along the inner periphery of the intake pipe on the upstream side, can be trapped in the annular space. Thus, the throttle valve 104 can be restricted from being frozen to the surface of the throttle bore formed in the bore inner pipe 102. Furthermore, the throttle body 101 is formed of resin, so that manufacturing cost and weight of the throttle body 101 can be reduced. In this structure, deformation in the throttle body 101, which is caused due to contraction after molding and/or assembling, do not directly exert influence against the inner diametrical dimension of the throttle bore in the bore inner pipe 102, even when the throttle body 101 is molded of thermoplastic resin in an injection molding die. Thereby, accuracy of the inner diametrical dimension of the throttle bore of the bore inner pipe 102 can be enhanced.
A driving unit, which operates the throttle valve 104 and a throttle shaft 105, is constructed of a motor, i.e., a power source 106 and a transmission mechanism (reduction gears), which transmits rotation power of the motor 106 to the throttle valve 104. The reduction gears are constructed of a pinion gear 110, an intermediate gear 111, and a valve gear 112. The pinion gear 110 is fixed to a motor shaft 109 of the motor 106. The intermediate gear 111 engages with the pinion gear 110 to be rotated. The valve gear 112 engages with the intermediate gear 111 to be rotated. A throttle opening sensor is mounted to the outer wall of the throttle body 101. The throttle opening sensor includes a permanent magnet 113 and a non-contact type magnetism detecting element 114. The permanent magnet 113 is secured to the inner periphery of the valve gear 112, which is connected to one axial end of the throttle shaft 105. The magnetism detecting element 114 generates electromotive force in accordance with a magnetic field generated by the permanent magnet 113. The magnetism detecting element 114 is fixed to a sensor mount part 116 provided to a sensor cover 115, which is connected to the outer wall of the throttle body 101, in a manner to be arranged in opposition to the inner peripheral surface of a yoke, which is magnetized by the permanent magnet 113. A return spring 117 is provided to a gap between the bore outer pipe 103 and the valve gear 112 to bias the throttle valve 104 to the side, in which the throttle valve 104 is closed.
A cylindrical motor housing portion 122 and a gearbox portion 124 are formed of resin integrally with the outer wall of the bore outer pipe 103 in the throttle body 101. The motor housing portion 122 has a motor accommodating hole 121, in which the motor 106 is accommodated. The gearbox portion 124 has a gear chamber 123 that rotatably accommodates the reduction gears. Here, vibration of the engine is directly transmitted to the throttle body 101. Therefore, as shown in FIGS. 6 to 8, multiple reinforcement ribs 125 are formed integrally with the outer periphery of the sidewall of the motor housing portion 122 along the axial direction of the motor accommodating hole 121, for example. Besides, multiple reinforcement ribs 125 are radially formed integrally with the outer periphery of the bottom wall of the motor housing portion 122, for example. Thereby, rigidity of the motor housing portion 122, which accommodates the motor 106, is enhanced to be sustainable against vibration of the engine. In the throttle body 101, the outer wall of the bore outer pipe 103 and the sidewall of the motor housing portion 122 are directly connected via multiple housing connecting ribs 127, which are formed of multiple plate-shaped connecting ribs, to reduce vibration of the motor 103.
In the above conventional structure, the outer wall of the bore outer pipe 103 of the throttle body 101, which has the double pipe structure, and the sidewall of the motor housing portion 122 are connected via the housing connecting ribs 127. However, the housing connecting ribs 127 needs to support the motor housing portion 122, which accommodates the motor 106 heavier than the resinous throttle body 101. Accordingly, the housing connecting ribs 127 need to be sufficiently rigid. Therefore, the thickness of the housing connecting ribs 127 is increased to reinforce the housing connecting ribs 127. Besides, the housing connecting ribs 127, which are provided along the axial direction of the bore outer pipe 103, are formed to have the width thereof (FIGS. 7, 8), which is equivalent to the diameter of the motor housing portion 122, to reinforce the housing connecting ribs 127.
However, in this structure, deformation in the motor housing portion 122 such as contract after forming thereof may be propagated to the bore inner pipe 102 via the housing connecting ribs 127, the bore outer pipe 103 and an annular connecting portion that connects the outer periphery of the bore inner pipe 102 with the inner periphery of the bore outer pipe 103. Besides, when a flange portion 129, which is integrally formed with an axial end of the bore outer pipe 103, is mounted to a bracket, which is fixed to the intake manifold of the engine in the vehicle, the flange portion 129 may deform. The deformation of the flange portion 129 may be propagated to the bore inner pipe 102 via the annular connecting portion. In these situations, the throttle bore in the bore inner pipe 102 may be degraded in dimensional accuracy. Accordingly, the throttle bore deforms in the bore inner pipe 102, and the roundness of the throttle bore deteriorates. As a result, air tightness of the throttle valve 104 in the full-closing position may be degraded, and a leakage amount of intake air increases in the full-closing position in an idling operation. Accordingly, the idling speed may become larger than a predetermined idling speed, and fuel consumption may increase in the idling operation.
Furthermore, when the throttle bore of the bore inner pipe 102 becomes out of a predetermined roundness, the throttle bore may interfere with the outer periphery of the throttle valve 104, when the throttle valve 104 is rotated. In this case, the throttle valve 104 may not be properly operated, and a valve-lock, i.e., seizure may be caused in the throttle valve 104. As a result, the throttle opening degree may not conform to the accelerator position, and drivability may be degraded.